Method for producing purified dialkyl-furan-2,5-dicarboxylate by physical separation and solid liquid separation

ABSTRACT

A process to produce a purified dimethyl-furan-2,5-dicarboxylate (DMFD) by feeding furan dicarboxylic acid and methanol to an esterification zone to generate a crude diester composition, and purifying the crude diester composition with a physical separation process followed by crystallization, solid liquid separation, and optionally drying to produce a purified DMFD composition. A portion of the stream generated by solid liquid separation can be dissolved and subjected to crystallization and solid liquid separation repeatedly. The process is useful to produce a purified DMFD composition having a low b*, at least 98 wt. % DAFD solids, and a low concentration of 5-(methoxycarbonyl)furan-2-carboxylic acid (MCFC) and methyl 5-formylfuran-2-carboxylate (MFFC).

1. CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/530,765, filed Jun. 22, 2012. The entire disclosure of theabove-referenced application is incorporated herein by reference.

2. FIELD OF THE INVENTION

The invention relates to the processes for the production of purifieddialkyl-furan-2,5-dicarboxylate (DAFD) and purified DAFD compositionsmade therefrom.

3. BACKGROUND OF THE INVENTION

Aromatic dicarboxylic acids such as terephthalic acid and isophthalicacid or their di-esters, dimethyl terephthalate as for example, are usedto produce a variety of polyester products, important examples of whichare poly (ethylene terephthalate) and its copolymers. The aromaticdicarboxylic acids are synthesized by the catalytic oxidation of thecorresponding dialkyl aromatic compounds which are obtained from fossilfuels such as those disclosed in US 2006/0205977 A1. Esterification ofthese diacids using excess alcohol produces the corresponding di-estershas been disclosed in US2010/0210867A1. There is a growing interest inthe use of renewable resources as feed stocks for the chemicalindustries mainly due to the progressive reduction of fossil reservesand their related environmental impacts.

Furan-2,5-dicarboxylic acid (“FDCA”) is a versatile intermediateconsidered as a promising closest biobased alternative to terephthalicacid and isophthalic acid. Like aromatic diacids, FDCA can be condensedwith diols such as ethylene glycol to make polyester resins similar topolyethylene terephthalate (PET) as disclosed in Gandini, A.; Silvestre,A. J; Neto, C. P.; Sousa, A. F.; Gomes, M. J. Poly. Sci. A 2009, 47,295. FDCA has been prepared by oxidation of 5-(hydroxymethyl) furfural(5-HMF) under air using homogenous catalysts as disclosed inUS2003/0055271 A1 and in Partenheimer, W.; Grushin, V. V. Adv. Synth.Catal. 2001, 343, 102-111. However, achieving high yields has proveddifficult. A maximum of 44.8% yield using Co/Mn/Br catalysts system anda maximum of 60.9% yield was reported using Co/Mn/Br/Zr catalystscombination.

The crude FDCA obtained by the oxidation processes must to be purifiedbefore they are suitable for end-use applications. JP patentapplication, JP209-242312A, disclosed crude FDCA purification processusing sodium hydroxide/sodium hypochlorite and/or hydrogen peroxidefollowed by acid treatment of the disodium salt to obtain pure FDCA.This multi-step purification process generates wasteful by-products, isdifficult to scale up to a commercial process, and poses safety concernsat large scales.

Therefore, there is a need for an inexpensive and high yield process forthe purification of crude FDCA that lends itself more readily to acommercial scale process and lends itself to easy separation step(s).

4. SUMMARY OF THE INVENTION

There is now provided a process for the manufacture of a DAFDcomposition comprising:

-   -   a. feeding a furan-2,5-dicarboxylic acid (“FDCA”) composition to        an esterification reactor; and    -   b. in the presence of an alcohol compound, conducting an        esterification reaction in the esterification reactor to react        FDCA with said alcohol compound to form a crude diester        composition comprising dialkyl furan-2,5-dicarboxylate (“DAFD”)        and the alcohol compound; and    -   c. separating at least a portion of alcohol compound from the        crude diester composition in an alcohol separation zone using a        physical separation process to produce a DAFD rich composition        comprising DAFD solids, wherein the concentration of DAFD in the        DAFD rich composition is higher than the concentration of DAFD        in the crude diester composition on a combined solid and liquid        basis; and    -   d. treating the DAFD rich composition in a purification zone to        produce a purified DAFD product composition.

There is also provided a process for the preparation of the FDCA fed tothe esterification reaction zone.

There is also provided a DAFD composition comprising:

-   -   (i) at least 98 wt. % solids based on the weight of the        composition, said solids comprising DAFD in an amount of greater        than 98 wt. % based on the weight of the solids,    -   (ii) a b* of 5 or less,    -   (iii) not more than 3 wt. % 5-(alkoxycarbonyl)furan-2-carboxylic        acid (ACFC), and    -   (iv) not more than 3 wt. % alkyll 5-formylfuran-2-carboxylate        (AFFC).

The is also provided a process that forms a very pure DAFD compositionon a commercial scale. The process is for the manufacture of a dialkylfuran-2,5-dicarboxylate (DAFD) composition having a throughput of atleast 1000 kg/day for any 30 days on a 24 hour/day basis, said processcomprising:

-   -   a. esterifying furan-2,5-dicarboxylic acid (“FDCA”) with an        alcohol in an esterification vessel to form a crude diester        composition having a b* and comprising unreacted alcohol, water,        dialkyl furan-2,5-dicarboxylate (“DAFD”);        5-(alkoxycarbonyl)furan-2-carboxylic acid (ACFC); alkyll        5-formylfuran-2-carboxylate (AFFC); and    -   b. purifying the crude diester composition to form a purified        DAFD product composition, wherein the purified DAFD product        composition has:        -   i. a b* that is lower than the b* of the crude diester            composition by at least 1 b* unit; and        -   ii. a higher DAFD concentration than the DAFD concentration            in the crude diester composition by at least 200%; and        -   iii. a lower ACFC concentration than the concentration of            ACFC in the crude diester composition by at least 70%,            without taking into account the amount of alcohol in the            crude diester composition; and        -   iv. a lower AFFC concentration than the concentration of            AFFC in the crude diester composition by at least 70%.

5. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of the process for making both FDCA and DAFD.

FIG. 2 is a flow diagram describing the feed of raw materials to theesterification reactor.

FIG. 3 is a flow diagram depicting the process of crystallizing, solidliquid separation, and isolating a DAFD composition, and optionallydissolving and subjecting the dissolved composition again tocrystallization.

FIG. 4 is a flow diagram describing repeated stages of crystallization,solid liquid separation, and dissolution until the desired crystalpurity is obtained.

6. DETAILED DESCRIPTION OF THE INVENTION

It should be understood that the following is not intended to be anexclusive list of defined terms. Other definitions may be provided inthe foregoing description, such as, for example, when accompanying theuse of a defined term in context.

As used herein, the terms “a,” “an,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination, B and C in combination; orA, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise” providedabove.

As used herein, the terms “including,” “includes,” and “include” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claim limitations that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

The present description uses specific numerical values to quantifycertain parameters relating to the invention, where the specificnumerical values are not expressly part of a numerical range. It shouldbe understood that each specific numerical value provided herein is tobe construed as providing literal support for a broad, intermediate, andnarrow range. The broad range associated with each specific numericalvalue is the numerical value plus and minus 60 percent of the numericalvalue, rounded to two significant digits. The intermediate rangeassociated with each specific numerical value is the numerical valueplus and minus 30 percent of the numerical value, rounded to twosignificant digits. The narrow range associated with each specificnumerical value is the numerical value plus and minus 15 percent of thenumerical value, rounded to two significant digits. For example, if thespecification describes a specific temperature of 62° F., such adescription provides literal support for a broad numerical range of 25°F. to 99° F. (62° F.+1-37° F.), an intermediate numerical range of 43°F. to 81° F. (62° F.+1-19° F.), and a narrow numerical range of 53° F.to 71° F. (62° F.+1-9° F.). These broad, intermediate, and narrownumerical ranges should be applied not only to the specific values, butshould also be applied to differences between these specific values.Thus, if the specification describes a first pressure of 110 psia and asecond pressure of 48 psia (a difference of 62 psia), the broad,intermediate, and narrow ranges for the pressure difference betweenthese two streams would be 25 psia to 99 psia, 43 psia to 81 psia, and53 psia to 71 psia, respectively

The word “rich” in reference to a composition means the concentration ofthe referenced ingredient in the composition is higher than theconcentration of the same ingredient in the feed composition to theseparation zone by weight. For example, a DAFD rich composition meansthat the concentration of DAFD in the DAFD rich composition is greaterthan the concentration of DAFD in the crude diester stream feeding theseparation zone.

All amounts are by weight unless otherwise specified.

As illustrated in FIG. 1, a dicarboxylic acid composition stream 410,which can be either dried carboxylic acid solids or a wet cakecontaining carboxylic acid, in each case the carboxylic acid comprisingfuran dicarboxylic acid (“FDCA”), and an alcohol composition stream 520are fed to the esterification reaction zone 500. The solid dicarboxylicacid composition 410 can be shipped via truck, ship, or rail as solidsto a plant or facility for the manufacture of the diester composition.The process for the oxidation of the oxidizable material containing thefuran group can be integrated with the process for the manufacture ofthe diester composition. An integrated process includes co-locating thetwo manufacturing facilities, one for oxidation and the other foresterification, within 10 miles, or within 5 miles, or within 2 miles,or within 1 mile, or within ½ mile of each other. An integrated processalso includes having the two manufacturing facilities in solid or fluidcommunication with each other. If a solid dicarboxylic acid compositionis produced, the solids can be conveyed by any suitable means, such asair or belt, to the esterification facility. If a wet cake dicarboxylicacid composition is produced, the wet cake can be moved by belt orpumped as a liquid slurry to the facility for esterification.

The esterification zone 500 contains at least one esterification reactorvessel. The dicarboxylic acid composition comprising FDCA is fed to theesterification zone and, in the presence of an alcohol compound, anesterification reaction is conducted in an esterification reactor byreacting FDCA with said alcohol compound to form a crude diestercomposition comprising dialkyl furan-2,5-dicarboxylate (“DAFD”), thealcohol compound, 5-(alkoxycarbonyl)furan-2-carboxylic acid (ACFC),alkyl furan-2-carboxylate (AFC), and alkyl-5-formylfuran-2-carboxylate(AFFC). The crude diester composition may optionally contain a catalystif a homogeneous esterification catalyst is used.

The alcohol composition is one or more types of alcohol compounds.Examples include compounds represented by the structure R—OH wherein Rcan range from 1 to 6 carbons, or 1 to 5 carbon atoms, or 1 to 4 carbonatoms, or 1 to 3 carbon atoms, or 1 to 2 carbon atoms, preferablymethanol. R can be branched or unbranched, saturated or unsaturated, andcyclic or acyclic. Desirably, R is an unbranched, saturated, acyclicalkyl group. The alcohol composition contains at least 50 wt. %, or atleast 60 wt %, or at least 70 wt %, or at least 80 wt. %, or at least 90wt. %, or at least 95 wt %, or at least 97 wt %, or at least 98 wt. %,or at least 99 wt. % alcohol compounds based on the weight of thealcohol composition. Desirably, the alcohol composition comprisesmethanol.

The crude diester composition produced in the esterification reactor isthe reaction product of at least FDCA with the alcohol composition toproduce DAFD, where the alkyl moiety is an alkyl group containing 1 to 6carbon atoms, and at least a portion of the alkyl moiety corresponds tothe alcohol residue. In the case of a reaction between FDCA andmethanol, the diester reaction product is dimethylfuran-2,5-dicarboxylate (“DMFD”). The esterification reaction of FDCAwith methanol to produce DMFD comprises multiple reaction mechanisms asillustrated below. One reaction mechanism comprises reacting one mole ofFDCA with one mole of MeOH to produce a mole of5-(methoxycarbonyl)furan-2-carboxylic acid (MCFC) and water. One mole ofMCFC can then react with one mole of methanol to produce one mole of thedesired product DMFD and water. Because both DMFD and MCFC are presentin an esterification reaction zone, the crude diester composition willalso contain MCFC in addition to the unreacted hydroxyl compounds andDAFD. A commercial process to produce purified DMFD must allow for theseparation of DMFD and MCFC downstream of the esterification zone. Anexample of a batch result for esterification of crude FDCA with methanolis given in the experimental section.

Esterification by-products are also formed in esterification reactorreaction zone 500 and comprise chemicals with boiling points both higherand lower than DMFD. Esterification by-products formed in theesterification reaction zone comprise methyl acetate, alkylfuran-2-carboxylate (AFC), alkyll 5-formylfuran-2-carboxylate (AFFC),and 5-(alkoxycarbonyl)furan-2-carboxylic acid (ACFC). Many otherby-products are possible depending upon the impurities contained withinthe FDCA feedstock. A commercial process to produce a purified DAFDstream must allow for the separation of impurities from the crudedi-ester composition exiting as stream 510. Further, at least a portionof these impurities can be purged from the process wherein purginginvolves isolation of the impurities and routing them from the process.

It is desirable to first mix the solid dicarboxylic acid compositionwith the alcohol prior to conducting an esterification reaction underesterification conditions. As illustrated in FIG. 2, there is provided amixing zone 540 and esterification reactor 550 within the esterificationzone 500. The solid dicarboxylic acid composition 410 comprising FDCA,an fresh or virgin feed of an alcohol composition as stream 520,optionally an alcohol recycle stream 802 comprising a recycled alcoholat least one of which is the same type of compounds as fed in stream520, an optional esterification catalyst composition stream 530, are fedinto the mixing zone 540 to generate mixed reactor feed stream 501. Inone embodiment, streams 802 and 520 comprise methanol.

Mixing in zone 540 may be accomplished by any equipment known in the artfor mixing liquid and solids, such as continuous in line static mixers,batch agitated vessels, and or continuous agitated vessels, and thelike. The theoretical amount of alcohol required for the reaction witheach mole of FDCA is two moles. The total amount of alcohol present inthe esterification reactor 550 is desirably in excess of the theoreticalamount required for the esterification reaction.

For example, the molar ratio of alcohol to FDCA moles ranges fromgreater than 2:1, or at least 2.2:1, or at least 2.5:1, or at least 3:1,or at least 4:1, or at least 8:1, or at least 10:1, or at least 15:1, orat least 20:1, or at least 25:1, or at least 30:1 and can go as high as40:1. Suitable molar ratios are within a range of alcohol to FDCA from10:1 to 30:1.

To the mixing zone is also optionally fed an esterification catalystsystem as stream 530 if a catalyst is used. The catalyst is can beheterogeneous in a fixed bed or desirably a homogenous catalyst underesterification reaction conditions, and can also be homogeneous in themixing zone. Known organometallic esterification catalysts can be usedsuch as the acetate of cobalt, copper and manganese, and zinc in amountsconventionally used for esterifying terephathalic acid. Other organiccatalysts can be employed such as sulfuric acid

Suitable quantities of esterification catalyst range from 0.1 wt. % to5.0 wt. %, or 0.5 wt. % to 2.0 wt. %, based on the weight of DAFD feed.

The mixed reactor feed stream 501 is routed to esterification reactor550 to generate a crude diester composition exiting the esterificationreactor as liquid crude diester stream 510. The crude diestercomposition, before separation of alcohol and water, desirably containsDAFD present in an amount of at least 5 wt %, or at least 8 wt. %, or atleast 10 wt. %, or at least 15 wt. %, or at least 20 wt. %, and up to 40wt. %, or up to 35 wt. %, based on the liquid phase weight of the crudediester composition. At the high temperatures, high pressure, and/orhigh alcohol concentration in esterification conditions, the DAFDpresent in the crude diester composition is solubilized and the solidsconcentration is generally not more than 5 wt. %, or not more than 2 wt.%, or not more than 1 wt. %, or not more than 0.5 wt. %, or not morethan 0.1 wt. %, although the amount of solids can be higher as theconcentration of unreacted alcohol is diminished and the reactiontemperature is reduced. If solids are present, at least 99 wt. % of thesolids are unreacted FDCA solids.

The yield of DAFD in the crude diester composition desirably high.Suitable yields are at least 55 mole %, or at least 60 mole %, or atleast 65%, or at least 70 mole %, or at least 75 mole %, or at least 80mole %, or at least 85 mole %, or at least 90 mole %, or at least 95mole %, or at least 99 mole %. The yield of DAFD in the crude diesterstream is calculated as follows:

mol of DAFD in the crude diester composition in the liquidphase/starting mol of FDCA)*100%.

The FDCA slurry stream can be fed into the esterification reactor at arate corresponding to a desired throughput in a continuous process forthe production of a purified DAFD product composition. Examples ofsuitable rates for the production of a purified DAFD product compositionstream include an average of at least 1000 kg/day, or at least 10,000kg/day, or at least 20,000 kg/day, or at least 50,000 kg/day, or atleast 75,000 kg/day, or at least 100,000 kg/day, or at least 200,000kg/day of a purified DAFD product composition, on a 24 hour basis overthe course of any three months.

Esterification may be accomplished in batch or continuous reactors andcomprises one or multiple reaction vessels that are capable of providingacceptable reaction residence time, temperature, and pressure. Theesterification reaction residence time ranges from 0.5 hr to about 10hours. The esterification temperature ranges from 150° C. to below thesupercritical temperature of the alcohol selected to ensure that thealcohol stays in liquid phase at reaction pressures. Suitable reactiontemperatures can range from 150° C. to 250° C., or 150° C. to 240° C.,or from 200° C. to 230° C. Particularly suitable is an upper range of240° C. in the case methanol is used as the alcohol. The esterificationpressure within the esterification reactor is sufficient to maintain thealcohol compound in the liquid phase and will vary with the temperatureselected. Suitable pressure ranges are from about 250 psig to about 2000psig, or from 400 psig to 1500 about psig.

The crude diester composition is taken from the esterification reactor550 as stream 510. As shown in FIG. 1, the crude diester compositionstream 510 is fed to an alcohol separation zone 600. At least a portionof alcohol compound in the crude diester composition 510 is separatedfrom the crude diester stream in the alcohol separation zone 600 in aphysical separation process to produce a DAFD rich composition stream620 containing liquid DAFD, and in which the concentration of DAFD inthe DAFD rich composition, on a liquid basis, is higher than theconcentration of DAFD in the crude diester composition on a liquidbasis.

The crude diester composition 510 exits the esterification zone 500 atelevated temperatures, typically at a temperature of at least 150° C.,or at least 170° C., or at least 180° C., or at least 190° C., or atleast 200° C., or at least 210° C., or at least 220° C., or at least230° C., or at least 240° C., and in each case below the supercriticaltemperature of the alcohol. To take advantage of the sensible heatenergy already present in crude diester composition, one may simplyconduct the physical separation under a pressure that is lower relativeto the pressure over the crude diester stream upon entry into theseparation zone, and thereby take off alcohol through reduced pressureto produce a DAFD-rich composition as stream 620. This can beaccomplished without applying additional heat energy to the separationvessel for separation purposes and thereby reduces energy consumption(e.g. adiabatic flash).

The alcohol separation zone 600 can comprise one or more vesselsoperated in series or parallel. For example, the alcohol separation zone600 can comprise one or more evaporative flash unit operations, or cancomprise one or more distillation columns. The alcohol separation zonecan comprise both a flash evaporation unit and a distillation column.The separation zone may be operated in a batch or continuous mode.

Desirably, the separation zone 600 contains at least a flash evaporationunit such as a flash tank. One may conduct staged flash evaporation inmultiple vessels. The pressure in the flash unit operation can rangefrom 0 psig to about 150 psig, or from 0 psig to about 50 psig, or from0 psig to 35 psig. If alcohol is separated under a reduced pressurerelative to the pressure of the crude diester composition at the entryto the physical separation vessel, it is desirable that the pressurewithin the alcohol separation vessel is below the vapor pressure of thealcohol at the temperature of the crude diester stream at the entry portto the alcohol separation vessel.

If desired, one does not have to first employ a flash evaporative unit.For example, the crude diester composition stream 510 can be feddirectly to a distillation column, heat energy is applied if necessaryto separate the alcohol from the crude diester composition, and thedistillate alcohol can be taken off as gaseous overhead, condensed andsent to the esterification zone as recycle stream 802. The bottoms ofthe distillation column are taken off as a DAFD rich composition stream620.

An alternative physical separation techniques is a membrane separationunit operation, which can be used alone or combination with at least oneflash unit operation, to generate alcohol gas composition stream 610 anda DAFD rich composition stream 620.

The temperature of the DAFD rich composition stream 620 exiting thealcohol separation zone 600 is not particularly limited. It will belower than the temperature of the crude diester stream entering thealcohol separation zone if evaporative separation techniques that do notapply external heat energy are used for the separation, such as a flashtank, due to evaporative cooling. However, if distillation techniquesare used, the temperature of the DAFD rich composition can be the sameor higher than the crude diester stream. In one embodiment, thetemperature of the DAFD rich composition stream 620 is at least 5° C.cooler, or at least 20° C. cooler, or at least 50° C. cooler, or atleast 75° C. cooler, or at least 100° C. cooler, or at least 120° C.cooler than the crude diester composition temperature entering thealcohol separation zone 600. If distillation is used, the DAFD richcomposition stream 620 can be at least 5° C. hotter, or at least 10° C.hotter than the temperature of the crude diester composition stream feedto the distillation column.

The alcohol that is flash evaporated or distilled exits the flash tankas an alcohol gas composition stream 610. The alcohol gas composition isdesirably taken as an overhead. As alcohol is flash evaporated, theconcentration of DAFD increases to form a DAFD rich stream. Theconcentration of water also increases in the DAFD rich stream relativeto the concentration of water in the crude diester composition. Sincethe solubility of DAFD in water is much less than DAFD in alcohol, aminor portion (e.g. less than 20 wt %) of the DAFD may precipitate outof solution. The alcohol gaseous overhead comprises alcohol, some water,and typically some very small (e.g. less than 0.1 wt %) DAFD can also bepresent.

The alcohol gas stream 610 can be condensed in the alcohol recovery zone800 and fed back to the esterification zone 500 as an alcohol recyclestream 802. This recycle stream may, however, contain some amount ofwater. If one desires to purify the alcohol gaseous stream 610 prior torecycling to esterification zone 500, it can be fed to at least onedistillation column in the alcohol recovery zone 800 to separate thealcohol compound as a distillate and recycled back to the esterificationzone 500, or used as a portion or all of the wash composition 732 to thesolid liquid separation zone(s), or used as a portion or all of thesolvent feed 1010 to the dissolving zone(s), or a combination of any ofthe foregoing feeds. The distillation column can be dedicated to receivea feed of the alcohol gaseous stream or the condensed alcohol effluent.The distillation column is operated to separate water from alcohol tofeed the esterification zone with the alcohol distillate as stream 802.The alcohol recycle stream 802 is desirably condensed to a liquid beforefeeding it to the mixing zone 540 or the esterification reactor 550.

Alternatively, the alcohol gaseous stream 610, or its condensate, can befed to a shared distillation column in alcohol recovery zone 800 thatalso receives feed 721, 741 and/or 742. It is desired to used a sharedcolumn to reduce capital costs. As shown in FIG. 1, a portion of all ofstream 721 can be fed first to a distillation column in alcohol recoveryzone 800.

The alcohol recycle stream 802 desirably contains less than 4 wt. %water, or less than 2 wt. % water, or less than 1 wt. % water, based onthe weight of the alcohol recycle stream 802. In one embodiment, alcoholrecycle stream 802 comprises methanol in an amount of at least 95 wt. %,or at least 98 wt. %, or at least 99 wt. %. Water composition stream 801is a liquid bottoms composition from a distillation column comprisingwater and DAFD. A portion of the water composition stream 801, up to 100wt %, can be routed from the process. A portion of the water compositionsteam 801, up to 100 wt %, can be recycled within the process to recoverat least a portion of the DAFD in stream 801. A portion of the watercomposition stream 801, up to 100 wt %, can be added to the DAFD richstream 620 or sent to purification zone 700. The DAFD rich compositionstream 620 comprises DAFD in a higher concentration that the amount ofDAFD present in the crude diester stream exiting the esterification zone500. The concentration of DAFD in the DAFD rich stream can be increasedby at or at least 20%, or at least 30%, or at least 40%, or at least50%, or at least 70%, or at least 90%, or at least 100%, or at least150%, or at least 200%, or at least 250%, or at least 300%, or at least400%, or at least 500%, over the concentration of DAFD in the crudediester composition. The DAFD rich stream desirably contains DAFDpresent in an amount of at least- or at least 10 wt %, or at least 20 wt%, or at least 30 wt %, or at least 40 wt %, or at least 50 wt %, or atleast 60 wt %, and in each case up to 70 wt. %, or up to 80 wt %, ineach case based on the weight of the DAFD rich composition. The DAFDrich stream desirably contains no solids. If present, the solidscomprise DAFD and/or unreacted FDCA. The solids concentration in theDAFD composition may contain no more than 55 wt. %, or up to 45 wt. %,or up to 35 wt. %, or up to 28 wt. %, or up to 15 wt. %, and if present,an amount of greater than zero, or at least 5 wt. %, or at least 10 wt.%, each based on the weight of the DAFD rich composition.

The DAFD rich composition stream 620 also contains any alcohol that didnot separate in the alcohol separation zone 600, water, and a quantityof some or all of the by-products mentioned above. The amount of alcoholin the DAFD rich stream can be at least 5 wt. %, or at least 10 wt. %,or at least 15 wt. %, and up to 60 wt. %, or up to 50 wt. %, or up to 40wt. %, based on the weight of the DAFD rich stream.

The DAFD rich composition depicted as stream 620 is fed to apurification zone 700. In the purification zone 700, the solids in theDAFD rich composition is fed to a solid liquid separation zone, wherethey are separated from the mother liquor and washed, to produce apurified DAFD product stream 710. Optionally the DAFD rich compositionis crystallized before solid-liquid separation. The DAFD richcomposition that is ultimately fed to the solid liquid separation zonegenerically includes all of the following steps: (i) a DAFD richcomposition that is fed to the solid-liquid separation zone withoutundergoing one or more dissolution and/or crystallization steps, (ii) aDAFD rich composition that undergoes one or more dissolution andcrystallization steps to produce a crystallized DAFD rich composition,and (iii) a DAFD rich composition that does not undergo dissolution butdoes undergo crystallization to produce a crystallized DAFD composition.

The purification zone 700 comprises at least a solid-liquid separationzone 713 as shown in FIG. 3. If desired, the purification zone may alsocomprise a crystallization zone 712, a dissolver zone 711, or both adissolver 711 and crystallization zone 712.

A portion of the purified DMFD composition stream 703 can optionally befed to an optional dissolver zone 711 along with an amount of a solventstream 1010 sufficient to redissolve at least a portion of the DAFDsolids in the purified DMFD composition. The solvent stream can be anysolvent effective to dissolve DAFD solids, including a fresh feed ofalcohol or a recycle feed of alcohol 802 obtained from the alcoholrecovery zone 800.

In the dissolving zone 711, at least a portion of solids present in thepurified DAFD composition 703 are dissolved. The purpose forre-dissolution of the solids after already having been subjected tosolid/liquid separation in zone 713 is to further purify the DAFD solidsif the level of by-products and impurities trapped within the solidsafter only one pass through the crystallizers remains undesirably high.By dissolution, such trapped by-products and impurities are liberatedback into solution.

The amount of solvent 1010 fed to the dissolving zone is dependent uponthe amount of solids one desires to dissolve, the solids concentrationof the purified DAFD composition, the temperature within the dissolutionzone, and the type of solvent used. It is desired to use sufficientsolvent under operating conditions effective to reduce the solidsconcentration by at least 80%, or at least 90%, or at least 95%, or atleast 98%, or at least 99%, or by 100%.

As shown in FIG. 3, the DAFD rich stream 620 is fed to a crystallizationzone 712. If a dissolution process is employed, the product of thedissolution zone, a dissolved DAFD rich composition 701, can be fed tothe crystallizer zone 712. The crystallization zone will generate acrystallized DAFD stream 702 comprising DAFD solids. At least a portionof DAFD in the DAFD rich stream 620, and at least a portion of the DAFDdissolved in the dissolved DAFD rich composition stream 701, comes outof solution to generate solid DAFD in crystallizer zone 712. In oneembodiment, at least 80 wt. %, or at least 90 wt. %, or at least 95 wt.%, or at least 98 wt. % of DAFD in the DAFD rich composition 620 comesout of solution to form DAFD solids in crystallized DAFD stream 702. Inanother embodiment, at least 80 wt. %, or at least 90 wt. %, or at least95 wt. %, or at least 98 wt. % of DAFD in the DAFD rich composition 620and dissolved DAFD rich composition stream 701 combined comes out ofsolution to form DAFD solids in crystallized DAFD stream 702.

Crystallization of DMFD in crystallization zone 712 may be accomplishedby any crystallizer design know in the art. Examples includeforced-circulation evaporative crystallizer, forced-circulation bafflesurface-cooled crystallizer, draft-tube baffle crystallizer, ordirect-contact refrigeration crystallizer. The crystallization zonecontains at least one crystallizer, and may contain multiplecrystallizers, e.g. 2-5 in series or multiple parallel trains.Generating DM FD solids from the optional dissolved DAFD richcomposition 701, or from the DAFD rich composition 620, in crystallizerzone 712 comprises cooling and/or adding an anti-solvent, and/orremoving a portion of the liquid continuous phase comprising the solvent(e.g. alcohol). If solvent is removed in crystallization zone 712 byevaporation, optionally under vacuum (e.g. lower than 1 atm), as ancrystallizer alcohol vapor stream 721, it can be recycled directly backto the esterification zone 500, or it can be sent to the alcoholseparation zone 800 for further purification before feeding it to theesterification zone 500, or it can be used as a wash stream in thesolid-liquid separation zone directly or after passing through thealcohol separation zone 800.

The operating temperature of the liquid within the crystallizationvessel can range from about 5° C. to about 100° C., or 15° C. to 65° C.,or 15° C. to about 35° C. The crystallization temperature can be stageddownward with each successive vessel if multiple vessels.

If desired, an anti-solvent composition stream 731 can be fed to acrystallizer in the crystallization zone 712. The anti-solventcomposition is a liquid that promotes crystallization and/orprecipitation of DAFD under the operating conditions in thecrystallizer. Such a stream can comprise water in an amount of at least50 wt. %, or at least 60 wt. %, or at least 70 wt. %, or at least 80 wt.%, or at least 90 wt. %, or at least 98 wt. %, or 100 wt. %, based onthe weight of the anti-solvent stream 731. The solubility of DMFD inmethanol and water varying temperature points ranging from about 1° C.to about 61° C. are set forth in Tables 3 and 4. DMFD has very lowsolubility in water compared to methanol so it operates as an excellentanti-solvent to promote crystallization.

From 1% to 45%, or from 3% to 35%, of the liquid in the DAFD rich stream620, and if present, in the dissolved DAFD rich composition stream 701,is removed by evaporation from the crystallization vessel incrystallizer zone 712. If desired, any combination of the cooling and oraddition of anti-solvent may be used, along with removing a portion ofthe liquid continuous phase.

The crystallized DAFD composition 702 comprises solids at aconcentration of at least 5 wt. %, or at least 10 wt. %, or at least 15wt. %, or at least 20 wt. %, and up to one's ability to pump the slurry,such as about up to 50 wt. %, or up to about 45 wt. %. The solidscomprise DAFD and the amount of DAFD present in the solids improves asone takes off a portion of the purified DAFD composition to cycle in adissolution and additional crystallization cycles. The amount of DAFDpresent in the solids is at least 90 wt. %, or at least 95 wt. %, or atleast 98 wt. %, or at least 99 wt. %, or at least 99.5 wt. %, or atleast 99.7 wt. %, or at least 99.8 wt. %, or at least 99.9 wt. %, or atleast 99.95 wt. %, or at least 99.97 wt. %, or at least 99.985 wt. %, orat least 99.99 wt. %, based on the weight of the crystallized DAFDcomposition.

The crystallized DMFD stream 702 produced in the crystallization zone712 is fed to a solid-liquid separation zone 713. To the solid-liquidseparation zone 713 is fed a wash solvent stream 732. A mother liquorstream 722, wash liquor stream 741 comprising wash solvent, and purifiedDAFD stream 703 are generated in the solid-liquid separation zone 713.

Solid-liquid separation zone 713 comprises at least one solid-liquidseparation device capable of separating solids and liquids, washingsolids with a wash stream 732, and reducing the percent moisture in thewashed solids to less than 50 wt. %, or less than 40 wt. %, or less than30 weight %, or less than 20 weight %, less than 15 weight %, andpreferably less than 10 weight % based on the weight of the purifiedDAFD composition stream 703.

The solid-liquid separation zone generates an esterification motherliquor stream 722 containing the solvent (e.g. alcohol) and by-productsand impurities. Desirably, the alcohol in esterification mother liquorstream 722 comprises methanol. Examples of by-products, or impurities,in mother liquor stream 722 comprise oxidation and or esterificationby-products. If desired, at least a portion of esterification motherliquor stream 722 can be directly fed back to the esterificationreaction zone 500. From 5% to 95%, from 30% to 90%, or from 40% to 80%of esterification mother liquor present in the crystallized DAFD streamfed to the solid-liquid separation zone 713 is isolated in theesterification mother liquor stream 722. The esterification motherliquor stream 722 contains dissolved impurities removed from the feed tothe solid liquid separation zone 713.

The wash stream 732 fed to and used as the wash feed for thecrystallized DAFD composition, comprises a liquid suitable fordisplacing and washing mother liquor from the solids. For example, thewash solvent may comprise water, alcohol, or water and alcohol, althoughthe solvent is not limited to the use of alcohols. It is desirable thatthe wash solvent contain a solvent miscible with the remaining alcoholin the crystallized DAFD composition, and can even be the same alcoholcompound. The wash solvent stream can comprise an alcohol present in anamount of at least 5 wt. %, or at least 10 wt. %, or at least 20 wt. %,or at least 40 wt. %, or at least 60 wt. %, or at least 80 wt. %, or atleast 90 wt. %, or at least 95 wt. % and the remainder, if any, can bewater. A mixture of alcohols can also be used.

The temperature of the wash solvent fed to the solid liquid separationzone is not limited, and can range from 10° C. up to below the boilingpoint of the wash solvent composition, or up to 50° or up to 40° C. Theamount of wash solvent used is defined as the wash ratio and equals themass of wash divided by the mass of solids on a batch or continuousbasis. The wash ratio, defined as the ratio of wash mass divided by themass of solids being washed, can range from 0.25 to 5, 0.3 to 4, and 0.4to 4. If desired, no wash is applied to solids in the solid liquidseparation zone 713.

The wash liquor stream 741 comprising at least a portion of the washsolvent and at least a portion of by-products is either purified andrecycled or exits the process as a waste stream.

Equipment suitable for solid liquid separation can include centrifugesof all types including but not limited to decanter and disc stackcentrifuges, solid bowl centrifuges, cyclone, rotary vacuum drum filter,vacuum belt filter optionally containing continuous co-current orcountercurrent washing steps, pressure leaf filter, candle filter, andthe like. The preferred solid liquid separation device for the solidliquid separation zone is a continuous pressure drum filter optionallywith multi-stage continuous co-current or countercurrent washing, ormore specifically a continuous rotary pressure drum filter. Thesolid-liquid separator may be operated in continuous or batch mode,although it will be appreciated that for commercial processes, thecontinuous mode is preferred.

One or more washes may be implemented in solid-liquid separation zone713. In one embodiment, one or more of the washes, preferably at leastthe final wash, in solid-liquid separation zone 713 may comprise adifunctional hydroxyl compound, such as ethylene glycol. By this method,a purified DAFD composition wet cake stream 703 is produced comprisingthe same hydroxyl functional compound in liquid form that would be usedin polymerization to make polyester containing FDCA moieties, and bythis method, the drying step in the product isolation zone 714 can beavoided. However, if one desires to produce a dried powder, then thewash liquids desirably are solvents that can easily volatize in a dryingstep and effective to wash the alcohol from the DAFD. Such wash solventsinclude methanol, ethanol, propanol and butanol.

The functions of washing and dewatering the crystallized DAFDcomposition stream may be accomplished in a single solid-liquidseparation device or multiple solid-liquid separation devices.

After solids are washed in the solid liquid separation zone 713, theyare dewatered. Dewatering can take place in the solid-liquid separationzone, and it can be part of or a separate device from the solid liquidseparation apparatus. Dewatering involves displacing and reducing atleast a portion of the mass of moisture of any composition present withthe solids to less than 50 wt. %, or less than 40 wt. %, or less than 30weight %, or less than 20 weight %, less than 15 weight %, andpreferably less than 10 weight % based on the weight of the purifiedDAFD composition stream 703. Dewatering can be accomplished by passing agas stream through the solids to displace free liquid after the solidshave been washed with a wash solvent. Alternatively, dewatering can beachieved by centrifugal forces in a perforated bowl or solid bowlcentrifuge.

The purified DAFD composition stream 703 can be in the form of a wetcake. All of the purified DAFD composition can be fed to the drying zoneto form dried particles or powder, or if a wet cake is desired as thefinal product, the drying zone can be by-passed or eliminated.

Optionally, a portion or all of the purified DAFD composition 703 can befed to the dissolver zone 711 for dissolution and re-crystallization. Asshown in FIG. 3, at least a portion of the purified DAFD compositionstream 703 is taken off as a feed to the dissolver zone 711. The solidsin the purified DAFD composition are redissolved in the dissolver zone711 and the dissolved DAFD rich composition 701 is fed as a recycle loopback to the crystallization zone 712 for re-crystallization of DAFD. Bythis method, the concentration of DAFD in the solids is increasedbecause a portion of the impurity by-products trapped in the DAFD solidsfrom the purified DAFD composition 703 are liberated into solution andafter another pass through the solid-liquid separation apparatus, aredirected into the mother liquor stream 722. One may take off a portionof the purified DAFD composition stream 703 continuously andre-circulate a portion of the dissolved stream 701 back to thecrystallization zone 712 continuously.

At least 2 wt. %, or at least 5 wt. %, or at least 10 wt. %, or at least15 wt. %, or at least 20 wt. %, or at least 30 wt. %, or at least 35 wt.%, or at least 40 wt. %, and up to 95 wt. %, or up to 90 wt. %, or up to85 wt. %, or up to 80 wt. %, or up to 75 wt. %, or up to 60 wt. %, or upto 50 wt. %, or up to 40 wt. %, or up to 30 wt. % of the purified DAFDcomposition may be taken off and fed to the dissolver zone 711.

If desired, one may take off at least a portion of the slurry from thesolid liquid separation zone 713 at any point after mother liquor stream722 has been separated from the crystallized DAFD rich composition 702.For example, a portion of the slurry may be taken off and fed to thedissolver zone 711 before the washing step in the solid liquidseparation zone 713. However, it is desirable that a portion of thecrystallized DAFD rich composition is taken off and fed to the dissolverzone 711 after the step of removing a mother liquor stream and after thecrystallized DAFD rich composition in the solid liquid separation zonehas been washed and before the final drying step in the solid liquidseparation zone. In this manner, the stream has been purified of atleast a portion of the by-product impurities by both separation andwashing.

If desired, the dissolved DAFD rich composition can be fed to a secondcrystallization zone instead of re-circulated back to the firstcrystallization zone 712. As shown in FIG. 4, the dissolved DAFD richcomposition 701 a can be fed to a n^(th) crystallization zone 712followed by feeding the n^(th) crystallized DAFD composition 702 n to ann^(th) solid-liquid separation zone 713. This process of dissolution andrecrystallization can be repeated until the desired purity is obtained.The distinction between a different zone and multiple crystallizersand/or solid liquid separation apparatus within a single zone is that adifferent zone is established when at least a portion of a feedcomposition in question is fed into two or more vessels which performthe same function. Multiple devices in series, however, do notconstitute multiple zones.

As shown in FIG. 4, the DAFD rich stream 620 is fed to a firstcrystallization zone 712 i. The product of the crystallization zone is acrystallized DAFD stream 702 a comprising DAFD solids. At least aportion of DAFD in the DAFD rich stream 620 comes out of solution togenerate solid DAFD in crystallizer zone 712 i. Solvent can be removedfrom the crystallization zone 712 by evaporation, optionally undervacuum (e.g. lower than 1 atm), as a crystallizer alcohol vapor stream721 i. The crystallized DMFD stream 702 a produced in thecrystallization zone 712 i is fed to a first solid-liquid separationzone 713 i. To the solid-liquid separation zone 713 i is fed a washsolvent stream 732. A first mother liquor stream 722 i, a first washliquor stream 741 i comprising wash solvent, and purified DAFDcomposition stream 703 a are generated in the solid-liquid separationzone 713 i. The esterification mother liquor stream 722 i containsdissolved impurities removed from the feed to the solid liquidseparation zone 713 i. The wash stream 732 fed to and used as the washfeed for the crystallized DAFD composition, comprises a liquid suitablefor displacing and washing mother liquor from the solids. The washliquor stream 741 i comprising at least a portion of the wash solventand at least a portion of by-products is either purified and recycled orexits the process as a waste stream. One or more washes may beimplemented in solid-liquid separation zone 713 i. After solids arewashed in the solid liquid separation zone 713 i, they are desirablydewatered. The purified DAFD composition stream 703 a can be in the formof a wet cake.

As shown in FIG. 4, a portion or all of the purified DAFD composition703 a can be fed to the first dissolver zone 711 i for dissolution usinga solvent feed 1010 to produce a product suitable forre-crystallization. At least a portion of the purified DAFD compositionstream 703 a is taken off as a dissolver feed 704 a to the firstdissolver zone 711 i. The solids in the dissolver feed 704 a (a portionor all of the purified DAFD composition) are redissolved in the firstdissolver zone 711 i to generate a dissolved DAFD rich composition 701 athat is fed into a nth crystallization zone 712 n for re-crystallizationof DAFD. “n” is an integer representing the number of cycles ofcrystallization, solid liquid separation, and dissolving, and each cycleis a nth vessel accepting a feed of material such that with eachadditional cycle, additional corresponding equipment is used to processthe feed. The designation “n” can be an integer from 0 to 5. Forexample, the nth crystallizer zone 712 n is a different zone from thefirst initial crystallizer zone 712 i in that at least a portion of thedissolved DAFD rich composition 701 a is fed to a differentcrystallization vessel within the nth crystallization zone 712 n thanthe crystallization vessel within the first initial crystallization zone712 i. By feeding into a different crystallization vessel, a second ornth crystallization zone is established.

When n=0, the nth crystallization zone 712 n and the nth solid liquidseparation zone 713 n and the nth dissolver zone 711 n are not presentand the dissolved DAFD rich composition 701 a is fed into the finalcrystallizer zone 712 f. When n=1, a third crystallization/solid liquidseparation is established (the initial 712 i/713 i plus the n=1 plus thefinal 712 f/713 f). When n=2, then four crystallization/solid liquidseparation zones are established, counting the initial and final zones,resulting if four cycles of crystallization and solid liquid separation.

Within the nth crystallization zone 712 n, the dissolved DAFD richcomposition 701 a is crystallized using an anti-solvent composition 731to generate a nth crystallized DAFD rich composition 702 n, where n isthe same integer as the “nth” integer of the nth crystallization zone712 n. The nth crystallized DAFD rich composition 702 n is fed to an nthsolid liquid separation zone 713 n to perform solid liquid separation,washing with a wash composition 732, and optional dewatering steps andthereby generate an nth mother liquor stream 722 n, an nth wash liquorstream 741 n, and an nth purified DAFD composition stream 703 n.

A portion of the nth purified DAFD composition stream 703 n may be takenoff and fed to the product isolation zone as shown in FIG. 4. A portionor all of the DAFD composition stream 703 n is fed to an nth dissolverzone 711 n as a nth dissolver feed 704 n for dissolution of at least aportion of the DAFD solids from the purified DAFD composition stream 703n. If n is an integer greater than 1, then a portion or all of the nthdissolved DAFD rich composition 701 n is fed to the nth crystallizerzone 712 n. The nth dissolved DAFD rich composition feeding through line701 n will commence the next succeeding higher digit of “n” to representthe next cycle and the additional crystallizer zone and solid liquidseparation zone. The number of additional crystallizer and solid liquidseparation zones can be any number ranging from 0 to 5 inclusive. Witheach new cycle, the process steps mentioned above are repeated.

Whether or not additional crystallizer and solid liquid separation zonesare established, a portion of the nth dissolved DAFD rich compositioncan be fed to the final crystallizer zone 712 f. If no additionalcrystallizer/solid liquid separation zone are employed, all of the nthdissolved DAFD rich composition can be fed to the final crystallizerzone 712 f. In the final crystallizer zone 712 f, the dissolved DAFDrich composition is crystallized to produce a final crystallized DAFDstream 702 f which is then fed to the final solid-liquid separation zone713 f to generate a final purified DAFD composition stream 703 f. Thefinal purified DAFD composition stream 703 f is fed, together with anynth purified DAFD composition streams 703 n if any, to the productisolation zone 714.

As shown in FIGS. 3 and 4, the purified DMFD composition stream 703, andif more than one cycle is employed, then 703 a and 703 f, is fed to theDMFD isolation zone 714 to produce DMFD product composition stream 710and a vapor stream 742 comprising primarily wash solvent and if presentsome mother liquor. In one embodiment, DMFD isolation zone 714 comprisesat least one dryer. Drying can be accomplished by any means known in theart that is capable of evaporating at least 50% of the volatilesremaining in the DMFD composition stream 703. For example, indirectcontact dryers including a rotary steam tube dryer, a Single ShaftPorcupine™ dryer, and a Bepex Solidaire™ dryer may be used. Directcontact dryers including a fluid bed dryer and drying in a convey linecan be used for drying. For both batch and continuous dryers, vacuum maybe applied to facilitate the removal of vapor from the dryer. A rotaryair lock valve may be used to continuously discharge the purified driedDMFD stream 710 from continuous dryers.

The percent solids in the DAFD product stream 710 can be at least 65 wt.%, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, orat least 90 wt. %, or at least 91 wt. %, or at least 92 wt. %, or atleast 93 wt. %, or at least 94 wt. %, or at least 95 wt. %, or at least99 wt. %, or at least 99.9 wt. %, or at least 99.99 wt. %.

In one embodiment, a vacuum system can be utilized to pull vapor stream742 from product isolation zone 714. If a vacuum system is used in thisfashion, the pressure of the vapor stream 742 at the dryer outlet canrange from about 760 mmHg to about 400 mmHg, from about 760 mmHg toabout 600 mmHg gauge, from about 760 mmHg to about 700 mmHg, from about760 mmHg to about 720 mmHg, or from about 760 mmHg to about 740 mmHg.The contents of the conduit between solid-liquid separation zone 713 andproduct isolation zone 714 utilized to transfer wet cake stream 703comprises wet cake stream 703 and gas wherein gas is the continuousphase. The pressure at the exit of the solid liquid separation zone 703can, if desired, be close to that of the pressure where vapor stream 742exits product isolation zone 714, wherein the close is defined as within2 psi, and can also be if desired within 0.8 psi, and preferably within0.4 psi.

In another embodiment, the solids in streams 703, 703 a, and 703 f canbe heated such that they melt and purified DMFD product stream 710 exitsthe process as a liquid melt without proceeding through or using adryer.

The vapor stream 742, mother liquor stream(s) 722, 722 n, 722 f, andvapor stream(s) 721, 721 i, and 721 f all contain alcohol and can be fedto an alcohol recovery zone 800 to generate recycle alcohol stream 802,and generating a water rich bottoms stream containing water and otherimpurities contained within the streams 742, 722, 722 i, 722 f, 721, 721i, and 721 f.

The DAFD product composition 710 desirably has a b* of no more than 15,or no more than 10, or no more than 5, or no more than 3, or no morethan 2, or no more than 1, or no more than 0.5.

The DAFD product composition desirably has a composition profile asfollows:

-   -   (i) at least 95 wt. % solids, or at least 98 wt. % solids, said        solids comprising DAFD in an amount of greater than 98 wt. %, or        at least 99 wt. %, or at least 99.5 wt. %, each based on the        weight of the solids;    -   (ii) a b* of 5 or less, or 4 or less, or 3 or less, or 2 or        less, and at least 0;    -   (iii) whether in the solid or liquid phase, not more than 3 wt.        % 5-(alkoxycarbonyl)furan-2-carboxylic acid (ACFC), or not more        than 2.5 wt. %, or not more than 2.0 wt. %, or not more than 1.8        wt. %, or not more than 1.5 wt. %, or not more than 1.3 wt. %,        or not more than 1.0 wt. %, or not more than 0.8 wt. %, or not        more than 0.6 wt. %, or not more than 0.3 wt % ACFC, or not more        than 1000 ppm ACFC, or not more than 500 ppm ACFC, or not more        than 250 ppm ACFC, based on the weight of the product        composition, and    -   (iv) whether in the solid or liquid phase, not more than 3.0 wt.        % alkyl 5-formylfuran-2-carboxylate (AFFC), or not more than 2.5        wt. %, or not more than 2.0 wt. %, or not more than 1.8 wt. %,        or not more than 1.5 wt. %, or not more than 1.3 wt. %, or not        more than 1.0 wt. %, or not more than 0.8 wt. %, or not more        than 1000 ppm, or not more than 500 ppm, or not more than 250        ppm AFFC, based on the weight of the product composition; and    -   (v) whether in the solid or liquid phase, not more than 1 wt. %        FDCA, or not more than 0.1 wt. % FDCA, or not more than 500 ppm        FDCA, or not more than 100 ppm FDCA, or not more than 10 ppm        FDCA, or not more than 1 ppm FDCA; and    -   (v) optionally not more than 1.5 wt. % water, or not more than        1.2 wt. %, or not more than 1.0 wt. %, or not more than 0.9 wt.        %, or not more than 0.8 wt. %, or not more than 0.7 wt. %, or        not more than 0.1 wt. %, or not more than 0.05 wt. %, or not        more than 0.02 wt. % water based on the weight of the product        composition.

The process of the invention is capable of improving the purity of thecrude diester composition on a commercial scale. It is now possible toproduce a purified DAFD product composition and DAFD product within theDAFD product composition at a rate of at least 1,000 kg/day, or at least3000 kg/day, or at least 5,000 kg/day, or at least 10,000 kg/day, or atleast 20,000 kg/day, or at least 50,000 kg/day, or at least 75,000kg/day, or at least 100,000 kg/day, or at least 200,000 kg/day, or atleast 400,000 kg/day, or at least 500,000 kg/day, on a 24 hour basisover the course of any three months.

The DAFD product composition produced at these rates desirably has alower b*, higher DAFD concentration, and lower ACCF and AFFCconcentration that each of their concentrations in the crude diestercomposition.

The DAFD product composition desirably has a b* that is lower than theb* of the crude diester composition by at least 1 b* unit, or at least 2b* units, or at least 3 b* units, or at least 4 b* units, or at least 5b* units, or at least 6 b* units.

The process of the invention is capable of improving the purity of thecrude diester composition by increasing the concentration of DAFD. TheDAFD product composition desirably has a higher DAFD concentration thanthe DAFD concentration in the crude diester composition by at least 20%,or at least 40%, or at least 50%, or at least 70%, or at least 80%, orat least 100%, or at least 120%, or at least 150%, or at least 200%, orat least 250%, or at least 300%, or at least 400%, or at least 500%, orat least 600%, or at least 700%, or at least 800%, or at least 900%,each as determined by taking the difference in the concentration betweenthe DAFD product composition and the crude diester composition dividedby the concentration of DAFD in the crude diester composition multipliedby 100, each on a weight basis. For example, final product DAFDconcentration of 99 wt. %, less a DAFD concentration in crude diestercomposition of 15 wt. % would equal 84 wt % divided by 15 wt%=5.6×100=560% increase.

The process of the invention is capable of improving the purity of thecrude diester composition by decreasing the concentration of ACFC. TheDAFD product composition desirably has a lower ACFC concentration thanthe concentration of ACFC in the crude diester composition. The DAFDproduct composition desirably has an ACFC concentration that is lowerthan the ACFC concentration in the crude diester composition, withouttaking into account the presence of the alcohol, by at least 20%, or atleast 40%, or at least 50%, or at least 70%, or at least 80%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99%, or at least 99.5%, as determined by taking the difference inthe concentration of ACFC in the DAFD product composition and theconcentration of the ACFC in the crude diester composition (calculatedwithout taking into account the amount of alcohol present in the crudediester composition) divided by the concentration of ACFC in the DAFDproduct composition multiplied by 100 and each taken on a weight basis.To describe the basis of the calculation, an example is as follows: theACFC concentration in the final product DAFD composition can be 0.02 wt% subtracted from the ACFC concentration in the crude diestercomposition which can be 1.2 wt % (the wt % of ACFC in the crude diestercomposition without accounting for the presence of alcohol)=1.18 wt %divided by 1.2 wt %=0.983×100=98.3% reduction.

The process of the invention is capable of improving the purity of thecrude diester composition by decreasing the concentration of AFFC. TheDAFD product composition desirably has a lower AFFC concentration thanthe concentration of AFFC in the crude diester composition. The DAFDproduct composition desirably has an AFFC concentration that is lowerthan the AFFC concentration in the crude diester composition, withouttaking into account the presence of the alcohol, by at least 20%, or atleast 40%, or at least 50%, or at least 70%, or at least 80%, or atleast 90%, or at least 95%, or at least 97%, or at least 98%, or atleast 99%, or at least 99.5%, as determined by taking the difference inthe concentration of AFFC in the DAFD product composition and theconcentration of the AFFC in the crude diester composition (calculatedwithout taking into account the amount of alcohol present in the crudediester composition) divided by the concentration of AFFC in the DAFDproduct composition multiplied by 100 and each taken on a weight basis.To describe the basis of the calculation, an example is as follows: theAFFC concentration in the final product DAFD composition can be 0.03 wt% subtracted from the AFFC concentration in the crude diestercomposition which can be 2.8 wt % (the wt % of AFFC in the crude diestercomposition without accounting for the presence of alcohol)=2.77 wt %divided by 2.8 wt %=0.989×100=98.9% reduction.

Advantageously, the esterification zone 500 is fed by a purified FDCAcomposition. The process for the manufacture of FDCA will now bedescribed in more detail.

The process comprises feeding an oxidizable composition to an oxidationzone, where the oxidizable composition contains a compound having afuran moiety. The furan moiety can be represented by the structure:

The compounds having a furan moiety are such that, upon oxidation, formcarboxylic acid functional groups on the compound. Examples of compoundshaving furan moieties include 5-(hydroxymethyl)furfural (5-HMF), andderivatives of 5-HMF. Such derivatives include esters of 5-HMF, such asthose represented by the formula 5-R(CO)OCH₂-furfural where R=alkyl,cycloalkyl and aryl groups having from 1 to 8 carbon atoms, or 1-4carbon atoms or 1-2 carbon atoms; ethers of 5-HMF represented by theformula 5-R′OCH₂-furfural, where R′=alkyl, cycloalkyl and aryl havingfrom 1 to 8 carbon atoms, or 1-4 carbon atoms or 1-2 carbon atoms);5-alkyl furfurals represented by the formula 5-R″-furfural, whereR″=alkyl, cycloalkyl and aryl having from 1 to 8 carbon atoms, or 1-4carbon atoms or 1-2 carbon atoms). Thus the oxidizable composition cancontain mixtures of 5-HMF and 5-HMF esters; 5-HMF and 5-HMF ethers;5-HMF and 5-alkyl furfurals, or mixtures of 5-HMF and its esters,ethers, and alkyl derivatives.

The oxidizable composition, in addition to 5-(hydroxymethyl)furfural(5-HMF) or an of its derivatives, may also contain5-(acetoxymethyl)furfural (5-AMF) and 5-(ethoxymethyl)furfural (5-EMF).

Specific examples of 5-HMF derivatives include those having thefollowing structures:

Preferred 5-HMF Derivative Feeds

One embodiment is illustrated in FIG. 1. An oxidizable composition isfed to a primary oxidation zone 100 and reacted in the presence of asolvent, a catalyst system, and a gas comprising oxygen, to generate acrude dicarboxylic acid stream 110 comprising furan-2,5-dicarboxylicacid (FDCA).

For example, the oxidizable composition containing 5-HMF, or itsderivatives, or combinations thereof, are oxidized with elemental O₂ ina multi-step reaction to form FDCA with 5-formyl furan-2-carboxylic acid(FFCA) as a key intermediate, represented by the following sequence:

If desired, the oxygen gas stream 10 comprising oxygen, a solvent stream30, and the oxidizable stream 20 can be fed to the primary oxidationzone 100 as separate streams. Or, an oxygen stream 10 comprising oxygenas one stream and an oxidizable stream 20 comprising solvent, catalyst,and oxidizable compounds as a second stream can be fed to the primaryoxidation zone 100. Accordingly, the solvent, oxygen gas comprisingoxygen, catalyst system, and oxidizable compounds can be fed to theprimary oxidization zone 100 as separate and individual streams orcombined in any combination prior to entering the primary oxidizationzone 100 wherein these feed streams may enter at a single location or inmultiple locations into the primary oxidizer zone 100.

The catalyst can be a homogenous catalyst soluble in the solvent or aheterogeneous catalyst. The catalyst composition is desirably soluble inthe solvent under reaction conditions, or it is soluble in the reactantsfed to the oxidation zone. Preferably, the catalyst composition issoluble in the solvent at 40° C. and 1 atm, and is soluble in thesolvent under the reaction conditions.

Suitable catalysts components comprise at least one selected from, butare not limited to, cobalt, bromine and manganese compounds. Preferablya homogeneous catalyst system is selected. The preferred catalyst systemcomprises cobalt, manganese and bromine.

The cobalt atoms may be provided in ionic form as inorganic cobaltsalts, such as cobalt bromide, cobalt nitrate, or cobalt chloride, ororganic cobalt compounds such as cobalt salts of aliphatic or aromaticacids having 2-22 carbon atoms, including cobalt acetate, cobaltoctanoate, cobalt benzoate, cobalt acetylacetonate, and cobaltnaphthalate. The oxidation state of cobalt when added as a compound tothe reaction mixture is not limited, and includes both the +2 and +3oxidation states.

The manganese atoms may be provided as one or more inorganic manganesesalts, such as manganese borates, manganese halides, manganese nitrates,or organometallic manganese compounds such as the manganese salts oflower aliphatic carboxylic acids, including manganese acetate, andmanganese salts of beta-diketonates, including manganeseacetylacetonate.

The bromine component may be added as elemental bromine, in combinedform, or as an anion. Suitable sources of bromine include hydrobromicacid, sodium bromide, ammonium bromide, potassium bromide, andtetrabromoethane. Hydrobromic acid, or sodium bromide may be preferredbromine sources.

The amount of bromine atoms desirably ranges from at least 300 ppm, orat least 2000 ppm, or at least 2500 ppm, or at least 3000 ppm, or atleast 3500 ppm, or at least 3750, ppm and up to 4500 ppm, or up to 4000ppm, based on the weight of the liquid in the reaction medium of theprimary oxidation zone. Bromine present in the an amount of 2500 ppm to4000 ppm, or 3000 ppm to 4000 ppm are especially desirable to promotehigh yield.

The amount of cobalt atoms can range from at least 500 ppm, or at least1500 ppm, or at least 2000 ppm, or at least 2500 ppm, or at least 3000ppm, and up to 6000 ppm, or up to 5500 ppm, or up to 5000 ppm, based onthe weight of the liquid in the reaction medium of the primary oxidationzone. Cobalt present in an amount of 2000 to 6000 ppm, or 2000 to 5000ppm are especially desirable to promote high yield.

The amount of manganese atoms can range from 2 ppm, or at least 10 ppm,or at least 30 ppm, or at least 50 ppm, or at least 70 ppm, or at least100 ppm, and in each case up to 600 ppm, or up to 500 ppm or up to 400ppm, or up to 350 ppm, or up to 300 ppm, or up to 250 ppm, based on theweight of the liquid in the reaction medium of the primary oxidationzone. Manganese present in an amount ranging from 30 ppm to 400 ppm, or70 ppm to 350 ppm, or 100 ppm to 350 ppm are especially desirable topromote high yield.

The weight ratio of cobalt atoms to manganese atoms in the reactionmixture can be from 1:1 to 400:1, or 10:1 to about 400:1. A catalystsystem with improved Co:Mn ratio can lead to high yield of FDCA. Toincrease the yield of FDCA, when the oxidizable composition fed to theoxidation reactor comprises 5-HMF, then the cobalt to manganese weightratio is at least 10:1, or at least 15:1, or at least 20:1, or at least25:1, or at least 30:1, or at least 40:1 or at least 50:1, or at least60:1, and in each case up to 400:1. However, in the case where theoxidizable composition comprises esters of 5-HMF, ethers of 5-HMF, or5-alkyl furfurals, or mixtures of any of these compounds together orwith 5-HMF, the cobalt to manganese weight ratio can be lowered whilestill obtaining high yield of FDCA, such as a weight ratio of Co:Mn ofat least 1:1, or at least 2:1, or at least 5:1, or at least 9:1, or atleast 10:1, or at least 15:1, or at least 20:1, or at least 25:1, or atleast 30:1, or at least 40:1, or at least 50:1, or at least 60:1 and ineach case up to 400:1.

The weight ratio of cobalt atoms to bromine atoms is desirably at least0.7:1, or at least 0.8:1, or at least 0.9:1, or at least 1:1, or atleast 1.05:1, or at least 1.2:1, or at least 1.5:1, or at least 1.8:1,or at least 2:1, or at least 2.2:1, or at least 2.4:1, or at least2.6:1, or at least 2.8:1, and in each case up to 3.5, or up to 3.0, orup to 2.8.

The weight ratio of bromine atoms to manganese atoms is from about 2:1to 500:1.

Desirably, the weight ratio of cobalt to manganese is from 10:1 to400:1, and the weight ratio of cobalt to bromine atoms ranges from 0.7:1to 3.5:1. Such a catalyst system with improved Co:Mn and Co:Br ratio canlead to high yield of FDCA (minimum of 90%), decrease in the formationof impurities (measured by b*) causing color in the downstreampolymerization process while keeping the amount of CO and CO₂ (carbonburn) in the off-gas at a minimum.

Desirably, the amount of bromine present is at least 1000 ppm and up to3500 ppm, and the weight ratio of bromine to manganese is from 2:1 to500:1. This combination has the advantage of high yield and low carbonburn.

Desirably, the amount of bromine present is at least 1000 ppm and up to3000 ppm, and the amount of cobalt present is at least 1000 ppm and upto 3000 ppm, and the weight ratio of cobalt to manganese is from 10:1 to100:1. This combination has the advantage of high yield and low carbonburn.

Suitable solvents include aliphatic solvents. In an embodiment of theinvention, the solvents are aliphatic carboxylic acids which include,but are not limited to, C₂ to C₆ monocarboxylic acids, e.g., aceticacid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid,trimethylacetic acid, caproic acid, and mixtures thereof.

The most common solvent used for the oxidation is an aqueous acetic acidsolution, typically having a concentration of 80 to 99 wt. %. Inespecially preferred embodiments, the solvent comprises a mixture ofwater and acetic acid which has a water content of 0% to about 15% byweight. Additionally, a portion of the solvent feed to the primaryoxidation reactor may be obtained from a recycle stream obtained bydisplacing about 80 to 90% of the mother liquor taken from the crudereaction mixture stream discharged from the primary oxidation reactorwith fresh, wet acetic acid containing about 0 to 15% water.

The oxidizing gas stream comprises oxygen. Examples include, but are notlimited to, air and purified oxygen. The amount of oxygen in the primaryoxidation zone ranges from about 5 mole % to 45 mole %, 5 mole % to 60mole % 5 mole % to 80 mole %.

The temperature of the reaction mixture in the primary oxidation zonecan vary from about 100° C. to about 220° C. The temperature of thereaction mixture in the primary oxidation zone is at least 100° C., orat least 105° C., or at least 110° C., or at least 115° C., or at least120° C., or at least 125° C., or at least 130° C., or at least 135° C.,or at least 140° C., or at least 145° C., or at least 150° C., or atleast 155° C., or at least 160° C., and can be as high as 220° C., or upto 210° C., or up to 200° C., or up to 195° C., or up to 190° C., or upto 180° C., or up to 175° C., or up to 170° C., or up to 165° C., or upto 160° C., or up to 155° C., or up to 150° C., or up to 145° C., or upto 140° C., or up to 135° C., or up to 130° C. In other embodiments, thetemperate ranges from 105° C. to 180° C., or from 105° C. to 175° C., orfrom 105° C. to 160° C., or from 105° C. to 165° C., or from 105° C. to160° C., or from 105° C. to 155° C., or from 105° C. to 150° C., or from110° C. to 180° C., or from 110° C. to 175° C., or from 110° C. to 170°C., or from 110° C. to 165° C., or from 110° C. to 160° C., or from 110°C. to 155° C., or from 110° C. to 150° C., or from 110° C. to 145° C.,or from 115° C. to 180° C., or from 115° C. to 175° C., or from 115° C.to 170° C., or from 115° C. to 167° C., or from 115° C. to 160° C., orfrom 115° C. to 155° C., or from 110° C. to 150° C., or from 115° C. to145° C., or from 120° C. to 180° C., or from 120° C. to 175° C., or from120° C. to 170° C., or from 120° C. to 165° C., or from 120° C. to 160°C., or from 120° C. to 155° C., or from 120° C. to 150° C., or from 120°C. to 145° C., or from 125° C. to 180° C., or from 125° C. to 175° C.,or from 125° C. to 170° C., or from 125° C. to 165° C., or from 125° C.to 160° C., or from 125° C. to 155° C., or from 125° C. to 150° C., orfrom 125° C. to 145° C., or from 130° C. to 180° C., or from 130° C. to175° C., or from 130° C. to 170° C., or from 130° C. to 165° C., or from130° C. to 160° C., or from 130° C. to 155° C., or from 130° C. to 150°C., or from 130° C. to 145° C., or from 135° C. to 180° C., or from 135°C. to 175° C., or from 135° C. to 170° C., or from 135° C. to 170° C.,or from 135° C. to 165° C., or from 135° C. to 160° C., or from 135° C.to 155° C., or from 135° C. to 150° C., or from 135° C. to 145° C., orfrom 140° C. to 180° C., or from 140° C. to 175° C., or from 140° C. to170° C., or from 140° C. to 170° C., or from 140° C. to 165° C., or from140° C. to 160° C., or from 140° C. to 155° C., or from 140° C. to 150°C., or from 140° C. to 145° C., or from 145° C. to 180° C., or from 145°C. to 175° C., or from 145° C. to 170° C., or from 145° C. to 170° C.,or from 145° C. to 165° C., or from 145° C. to 160° C., or from 145° C.to 155° C., or from 145° C. to 150° C., or from 150° C. to 180° C., orfrom 150° C. to 175° C., or from 150° C. to 170° C., or from 150° C. to165° C., or from 150° C. to 160° C., or from 150° C. to 155° C., or from155° C. to 180° C., or from 155° C. to 175° C., or from 155° C. to 170°C., or from 155° C. to 165° C., or from 155° C. to 160° C., or from 160°C. to 180° C., or from 160° C. to 175° C., or from 160° C. to 170° C.,or from 160° C. to 165° C., or from 165° C. to 180° C., or from 165° C.to 175° C., or from 165° C. to 170° C., or from 165° C. to 180° C., orfrom 165° C. to 175° C., or from 165° C. to 170° C., or from 170° C. to180° C., or from 170° C. to 175° C., or from 175° C. to 180° C.

To minimize carbon burn, it is desired that the temperature of thereaction mixture is not greater than 165° C., or not greater than 160°C. In the process of the invention, the contents of the oxidizer off gascomprise COx, wherein x is 1 or 2, and the amount of COx in the oxidizeroff gas is less than 0.05 moles of COx per mole of the total oxidizablefeed to the reaction medium, or no more than 4 moles of COx per mole ofthe total oxidizable feed to the reaction medium, or no more than 6moles of COx per mole of the total oxidizable feed to the reactionmedium. The carbon burn as determined by the COx generation rate can becalculated as follows: (moles of CO+moles of CO2)/moles of oxidizablefeed. The low carbon burn generation rate in the process of theinvention is achievable by the combination of low reaction temperature,and the molar weight ratios of the catalyst components as describedabove.

The oxidation reaction can be conducted under a pressure ranging from 40psia to 300 psia. A bubble column is desirably operated under a pressureranging from 40 psia to 150 psia. In a stirred tank vessel, the pressureis desirably set to 100 psia to 300 psia.

Oxidizer off gas stream 120 containing COx (CO and CO₂), water,nitrogen, and vaporized solvent, is routed to the oxidizer off gastreatment zone 800 to generate an inert gas stream 810, liquid stream820 comprising water, and a recovered oxidation solvent stream 830comprising condensed solvent. In one embodiment, oxidizer off gas stream120 can be fed to directly, or indirectly after separating condensablessuch as solvent from non-condensables such as COx and nitrogen in aseparation column (e.g. distillation column with 10-200 trays), to anenergy recovery device such as a turbo-expander to drive an electricgenerator. Alternatively or in addition, the oxidizer off gas stream canbe fed to a steam generator before or after the separation column togenerate steam, and if desired, may then be fed to a turbo-expander andpre-heated prior to entry in the expander if necessary to ensure thatthe off gas does not condense in the turbo-expander.

In another embodiment, at least a portion of the oxidation solventstream 830 recovered from the oxidizer off-gas stream is routed to afilter and then to a wash solvent stream 320 to become a portion of thewash solvent stream 320 for the purpose of washing the solids present inthe solid-liquid separation zone. In another embodiment, the inert gasstream 810 can be vented to the atmosphere. In yet another embodiment,at least a portion of the inert gas stream 810 can be used as an inertgas in the process for inerting vessels and or used for convey gas forsolids in the process.

The oxidation can be conducted in a continuous stirred tank reactor orin a bubble column reactor.

The FDCA formed by the oxidation reaction desirably precipitates out ofthe reaction mixture. The reaction mixture comprises the oxidizablecomposition, solvent, and catalyst if a homogeneous catalyst is used,otherwise it comprises the oxidizable composition and solvent.

The product of the oxidation reaction is a crude dicarboxylic acidstream 110 comprising FDCA as a solid, FDCA dissolved in the solvent,solvent, and by-products and intermediate products, and homogeneouscatalyst system if used. Examples of by-products include levulinic acid,succinic acid, and acetoxy acetic acid. Examples of intermediateproducts include 5-formyl furan-2-carboxylic acid (FFCA) and2,5-diformylfuran.

The percent solids in the crude dicarboxylic acid stream ranges is atleast 10 wt %, or at least 15 wt. %, or at least 20 wt. %, or at least25 wt. %, or at least 28 wt. %, or at least 30 wt. %, or at least 32 wt.%, or at least 35 wt. %, or at least 37 wt. %, or at least 40 wt. %.While there is no upper limit, as a practice the amount will not exceed60 wt. %, or no greater than 55 wt. %, or no greater than 50 wt. %, orno greater than 45 wt. %., or not greater than 43 wt. %, or not greaterthan 40 wt %, or not greater than 39 wr %.

The stated amount of each of the following intermediates, product, andimpurities are based on the weight of the solids in the crude carboxylicacid composition produced in the primary oxidation reactor in theoxidation zone 100.

The amount of the intermediate FFCA present in the crude dicarboxylicacid stream is not particularly limited. Desirably, the amount is lessthan 4 wt. %, or less than 3.5 wt. %, or less than 3.0 wt. %, or lessthan 2.5 wt. %, or up to 2.0 wt. %, or up to 1.5 wt. %, or up to 1.0 wt.%, or up to 0.8 wt. %.

Impurities, if present in the crude dicarboxylic acid composition,include such compounds as 2,5-diformylfuran, levulinic acid, succinicacid, and acetoxy acetic acid. These compounds can be present, if atall, in an amount of 0 wt % to about 0.2 wt % 2,5 diformylfuran,levulinic acid in an amount ranging from 0 wt % to 0.5 wt %, succinicacid in an amount ranging from 0 wt % to 0.5 wt % and acetoxy aceticacid in an amount ranging from 0 wt % to 0.5 wt %, and a cumulativeamount of these impurities in an amount ranging from 0 wt. % to 1 wt. %,or from 0.01 wt % to 0.8 wt. %, or from 0.05 wt % to 0.6 wt. %.

In another embodiment of the invention the carboxylic acid composition110 comprises FDCA, FFCA and 5-(ethoxycarbonyl)furan-2-carboxylic acid(“EFCA”). The EFCA in the carboxylic acid composition 110 can be presentin an amount of at least 0.05 wt %, or at least 0.1 wt %, or at least0.5 wt % and in each case up to about 4 wt %, or up to about 3.5 wt %,or up to 3 wt. %, or up to 2.5 wt %, or up to 2 wt. %.

The yield of FDCA, on a solids basis and measured after the drying zonestep, is at least 60%, or at least 65%, or at least 70%, or at least72%, or at least 74%, or at least 76%, or at least 78%, or at least 80%,or at least 81%, or at least 82%, or at least 83%, or at least 84%, orat least 85%, or at least 86%, or at least 87%, or at least 88%, or atleast 89%, or at least 90%., or at least 91%, or at least 92%, or atleast 94%, or at least 95%, and up to 99%, or up to 98%, or up to 97%,or up to 96%, or up to 95%, or up to 94%, or up to 93%, or up to 92%, orup to 91%, or up to 90%, or up to 89%. For example, the yield can rangefrom 70% up to 99%, or 74% up to 98%, or 78% up to 98%, or 80% up to98%, or 84% up to 98%, or 86% up to 98%, or 88% up to 98%, or 90% up to98%, or 91% up to 98%, or 92% up to 98%, or 94% up to 98%, or 95% up to99%.

Yield is defined as mass of FDCA obtained divided by the theoreticalamount of FDCA that should be produced based on the amount of rawmaterial use. For example, if one mole or 126.11 grams of 5-HMF areoxidized, it would theoretically generate one mole or 156.01 grams ofFDCA. If for example, the actual amount of FDCA formed is only 150grams, the yield for this reaction is calculated to be=(150/156.01)times 100, which equals a yield of 96%. The same calculation applies foroxidation reaction conducted using 5-HMF derivatives or mixed feeds.

The product purity of FDCA particles in a wet cake, or the purity ofFDCA dried solid particles, obtainable is at least 90 wt % FDCA, or atleast 92 wt % FDCA, or at least 94 wt % FDCA, or at least 96 wt % FDCA,or at least 98 wt % FDCA, based on the weight of the solids.

The maximum b* of the dried solids, or wet cake, is not particularlylimited. However, a b* of not more than 20, or no more than 19, or nomore than 18, or no more than 17, or no more than 16, or no more than15, or no more than 10, or no more than 8, or no more than 6, or no morethan 5, or no more than 4, or no more than 3, is desirable withouthaving to subject the crude carboxylic acid composition tohydrogenation. However, if lowered b* is important for a particularapplication, the crude carboxylic acid composition can be subjected tohydrogenation.

The b* is one of the three-color attributes measured on a spectroscopicreflectance-based instrument. The color can be measured by any deviceknown in the art. A Hunter Ultrascan XE instrument is typically themeasuring device. Positive readings signify the degree of yellow (orabsorbance of blue), while negative readings signify the degree of blue(or absorbance of yellow).

In the next step, which is an optional step, the crude dicarboxylic acidstream 110 can fed to a cooling zone 200 to generate a cooled crudedicarboxylic acid slurry stream 210 and a 1^(st) solvent vapor stream220 comprising solvent vapor. The cooling of crude carboxylic slurrystream 110 can be accomplished by any means known in the art. Typically,the cooling zone 200 is a flash tank. All or a portion of the crudedicarboxylic acid stream 110 can be fed to the cooling zone.

All or a portion of the crude dicarboxylic acid stream 110 can be fed tosolid-liquid separation zone 300 without first being fed to a coolingzone 200. Thus, none or only a portion can be cooled in cooling zone200. The temperature of stream 210 exiting the cooling zone can rangefrom 35° C. to 160° C., 55° C. to 120° C., and preferably from 75° C. to95° C.

The crude dicarboxylic acid stream 110, or 210 if routed through acooling zone, is fed to a solid-liquid separation zone 300 to generate acrude carboxylic acid wet cake stream 310 comprising FDCA. The functionsof isolating, washing and dewatering the crude carboxylic acid streammay be accomplished in a single solid-liquid separation device ormultiple solid-liquid separation devices. The solid-liquid separationzone 300 comprises at least one solid-liquid separation device capableof separating solids and liquids, washing solids with a wash solventstream 320, and reducing the % moisture in the washed solids to lessthan 30 weight %. Desirably, the solid-liquid separation device iscapable of reducing the % moisture down to less than 20 weight %, orless than 15 weight %, and preferably 10 weight % or less. Equipmentsuitable for the solid liquid separation zone can typically be comprisedof, but not limited to, the following types of devices: centrifuges ofall types including but not limited to decanter and disc stackcentrifuges, solid bowl centrifuges, cyclone, rotary drum filter, beltfilter, pressure leaf filter, candle filter, and the like. The preferredsolid liquid separation device for the solid liquid separation zone is acontinuous pressure drum filter, or more specifically a continuousrotary pressure drum filter. The solid-liquid separator may be operatedin continuous or batch mode, although it will be appreciated that forcommercial processes, the continuous mode is preferred.

The temperature of crude carboxylic acid slurry stream, if cooled asstream 210, fed to the solid-liquid separation zone 300 can range from35° C. to 160° C., 55° C. to 120° C., and is preferably from 75° C. to95° C. The wash stream 320 comprises a liquid suitable for displacingand washing mother liquor from the solids. For example, the wash solventcomprises acetic acid, or acetic acid and water, an alcohol, or water,in each case up to an amount of 100%. The temperature of the washsolvent can range from 20° C. to 180° C., or 40° C. and 150° C., or 50°C. to 130° C. The amount of wash solvent used is defined as the washratio and equals the mass of wash divided by the mass of solids on abatch or continuous basis. The wash ratio can range from about 0.3 toabout 5, about 0.4 to about 4, and preferably from about 0.5 to 3.

After solids are washed in the solid liquid separation zone 300, theyare dewatered. Dewatering can take place in the solid liquid separationzone or it can be a separate device from the solid-liquid separationdevice. Dewatering involves reducing the mass of moisture present withthe solids to less than 30% by weight, less than 25% by weight, lessthan 20% by weight, and most preferably less than 15% by weight so as togenerate a crude carboxylic acid wet cake stream 310 comprising FDCA.Dewatering can be accomplished in a filter by passing a gas streamthrough the solids to displace free liquid after the solids have beenwashed with a wash solvent. Alternatively, dewatering can be achieved bycentrifugal forces in a perforated bowl or solid bowl centrifuge.

One or more washes may be implemented in solid-liquid separation zone300. One or more of the washes, preferably at least the final wash, insolid-liquid separation zone 300 comprises a hydroxyl functionalcompound as defined further below, such as an alcohol (e.g. methanol).By this method, a wet cake stream 310 is produced comprising thehydroxyl functional compound such as methanol in liquid form. The amountof the hydroxyl functional compound in liquid form in the wet cake canbe at least 50 wt %, or at least 75 weight %, or at least 85% weight %,or at least 95 weight % hydroxyl functional compound such as methanolbased on the weight of the liquids in the wet cake stream. The advantageof adopting this technique of washing with a hydroxyl functionalcompound is that a portion or all of the wet cake can be fed to theesterification zone 500 without undergoing, or by-pass, a step offeeding the wet cake to a vessel for drying the wet cake in a dryingzone 400 after the solid-liquid separation zone.

In one embodiment, 100% of wet cake stream 310 is fed to esterificationreaction zone 500 without undergoing or subjecting the wet cake to avessel for drying the wet cake from the solid liquid separation zone300.

Stream 330 generated in solid-liquid separation zone 300 is a liquidmother liquor stream comprising oxidation solvent, catalyst, andimpurities. If desired, a portion of mother liquor stream 330 can be fedto a purge zone 900 and a portion can be fed back to the primaryoxidation zone 100, wherein a portion is at least 5 weight % based onthe weight of the liquid. Wash liquor stream 340 is also generated inthe solid-liquid separation zone 300 and comprises a portion of themother liquor present in stream 210 and wash solvent wherein the weightratio of mother liquor mass to wash solvent mass in the wash liquorstream is less than 3 and preferably less than 2. From 5% to 95%, from30% to 90%, and most preferably from 40% to 80% of mother liquor presentin the crude carboxylic acid stream fed to the solid-liquid separationzone 200 is isolated in solid-liquid separation zone 300 to generatemother liquor stream 330 resulting in dissolved matter comprisingimpurities present in the displaced mother liquor not going forward inthe process. The mother liquor stream 330 contains dissolved impuritiesremoved from the crude dicarboxylic acid.

Sufficient wash solvent is fed to the solid liquid separation zone 300that becomes mixed with solids present resulting in a low impurityslurry stream 310 being pumpable with weight % solids ranging from 1% to50%, 10% to 40%, and preferably the weight % solids in stream 310 willrange from 25% to 38%.

In one embodiment, from 5% to 100% by weight of the displaced motherliquor stream 330 is routed to a purge zone 900 wherein a portion of theimpurities present in stream 330 are isolated and exit the process aspurge stream 920, wherein a portion is 5% by weight or greater.Recovered solvent stream 910 comprises solvent and catalyst isolatedfrom stream 330 and is recycled to the process. The recovered solventstream 910 can be recycled to the primary oxidation zone 100 andcontains greater than 30% of the catalyst that entered the purge zone900 in stream 330. The stream 910 recycled to the primary oxidation zone100 may contain greater than 50 weight %, or greater than 70 weight %,or greater than 90 weight % of the catalyst that enters the purge zone900 in stream 330 on a continuous or batch basis.

Optionally, a portion up to 100% of the crude carboxylic acidcomposition may be routed directly to a secondary oxidation zone (notshown) before being subjected to a solid liquid separation zone 300.

Generally, oxidation in a secondary oxidation zone is at a highertemperature than the oxidation in the primary oxidation zone 100 toenhance the impurity removal. In one embodiment, the secondary oxidationzone is operated at about 30° C., 20° C., and preferably 10° C. highertemperature than the oxidation temperature in the primary oxidation zone100 to enhance the impurity removal. The secondary oxidation zone can beheated directly with solvent vapor, or steam via stream or indirectly byany means known in the art.

Additional purification of the crude carboxylic acid stream can beaccomplished in the secondary oxidation zone by a mechanism involvingrecrystallization or crystal growth and oxidation of impurities andintermediates including FFCA. One of the functions of the secondaryoxidation zone is to convert FFCA to FDCA. FFCA is consideredmonofunctional relative to a polyester condensation reaction because itcontains only one carboxylic acid. FFCA is present in the crudecarboxylic acid composition stream. FFCA is generated in the primaryoxidation zone 100 because the reaction of 5-HMF to FFCA can be abouteight times faster than the reaction of FFCA to the desireddi-functional product FDCA. Additional air or molecular oxygen may befed to the secondary oxidation zone in an amount necessary to oxidize asubstantial portion of the partially oxidized products such as FFCA tothe corresponding carboxylic acid FDCA. Generally, at least 70% byweight, or at least 80 wt %, or at least 90 wt % of the FFCA present inthe crude carboxylic acid composition exiting the primary oxidation zonecan be converted to FDCA in the secondary oxidation zone. Significantconcentrations of monofunctional molecules like FFCA in the dried,purified FDCA product are particularly detrimental to polymerizationprocesses as they may act as chain terminators during the polyestercondensation reaction.

If a secondary oxidation zone is employed, the secondary oxidationslurry can be crystallized to form a crystallized slurry stream. Vaporfrom the crystallization zone can be condensed in at least one condenserand returned to the crystallization zone or recycled, or it can bewithdrawn or sent to an energy recovery device. The crystallizer off-gascan be removed and routed to a recovery system where the solvent isremoved, and crystallizer off gas containing VOC's may be treated, forexample, by incineration in a catalytic oxidation unit. The crystallizercan be operated by cooling the secondary oxidation slurry to atemperature between about 40° C. to about 175° C. to form a crystallizedslurry stream.

The crystallized slurry stream can then be subjected to a cooling zone200 if desired and the process continued as described above.

Instead of using a wet cake, one may produce a dried solid. The wet cakeproduced in the solid liquid separation zone 300 can be dried in adrying zone 400 to generate a dry purified carboxylic acid solid 410 anda vapor stream 420. The vapor stream 420 typically comprises the washsolvent vapor used in the solid liquid separation zone, and mayadditionally contain the solvent used in the primary oxidation zone. Thedrying zone 400 comprises at least one dryer and can be accomplished byany means known in the art that is capable of evaporating at least 10%of the volatiles remaining in the purified wet cake stream to producethe dried, purified carboxylic acid solids. For example, indirectcontact dryers include, but are not limited to, a rotary steam tubedryer, a Single Shaft Porcupine dryer, and a Bepex Solidaire dryer.Direct contact dryers include, but are not limited to, a fluid bed dryerand drying in a convey line.

The dried, purified carboxylic acid solids comprising purified FDCA canbe a carboxylic acid composition with less than 8% moisture, preferablyless than 5% moisture, and more preferably less than 1% moisture, andeven more preferably less than 0.5%, and yet more preferably less than0.1%.

A vacuum system can be utilized to draw vapor stream 420 from the dryingzone 400. If a vacuum system is used in this fashion, the pressure atthe dryer outlet can range from about 760 mmHg to about 400 mmHg, fromabout 760 mmHg to about 600 mmHg, from about 760 mmHg to about 700 mmHg,from about 760 mmHg to about 720 mmHg, and from about 760 mmHg to about740 mmHg wherein pressure is measured in mmHg above absolute vacuum.

The dried, purified carboxylic acid solids, or the solids in the wetcake, desirably have a b* less than about 9.0, or less than about 6.0,or less than about 5.0, or less than about 4.0. or less than about 3.

It should be appreciated that the process zones previously described canbe utilized in any other logical order to produce the dried, purifiedcarboxylic acid. It should also be appreciated that when the processzones are reordered that the process conditions may change. It is alsounderstood that all percent values are weight percents.

One function of drying zone 400 is to remove by evaporation oxidationsolvent comprising a mono-carboxylic acid with 2 to 6 carbons that canbe present in the crude carboxylic acid wet cake stream 310. The %moisture in crude carboxylic acid wet cake stream 310 typically rangesfrom 4.0% by weight to 30% by weight depending on the operationconditions of the solid-liquid separation zone 300. If for example, theliquid portion of stream 310 is about 90% acetic acid, the amount ofacetic acid present in stream 310 can range from about 3.6 weight % to27 weight %. It is desirable to remove acetic acid prior toesterification zone 500 because acetic acid will react with the alcoholpresent in the zone 500 to create unwanted by products. For example, ifmethanol is fed to esterification zone 500 for the purpose of reactingwith FDCA, it will also react with acetic acid present to form methylacetate and therefore consume methanol and generate an unwantedby-product. It is desirable to minimize the acetic acid content of thecrude carboxylic acid stream comprising FDCA that is fed toesterification zone 500 to less than 3.6 weight %, preferably less than1 weight %, and more preferably less than 0.5 weight %, and mostpreferably less than 0.1 weight %. One method for achieving this is todry a crude carboxylic acid wet cake stream 310 comprising acetic acidprior to routing the crude carboxylic to esterification zone 500.Another method for minimizing the oxidation solvent comprisingmono-carboxylic acid with carbons ranging from 2 to 5 in the crudecarboxylic acid stream 410 routed to esterification zone 500 to anacceptable level without utilizing a dryer zone 400 is to conductnon-monocarboxylic acid wash or washes in solid-liquid separation zone300 to wash the oxidation solvent from the solids with a wash comprisingany wash solvent compatible with the esterification zone 500 chemistryto generate a crude carboxylic acid wet cake stream 310 suitable forrouting directly to esterification zone 500 without being dried indrying zone 400. Acceptable wash solvents comprise solvents that do notmake undesirable by products in esterification zone 500. For example,water is an acceptable wash solvent to displace acetic acid from solidsin solid-liquid separation zone 300. Another acceptable wash solvent isan alcohol that will be used as a reactant in the esterification zone500. There can be multiple and separate washes in the solid liquidseparation zone 300. A wash feed can comprise water up to 100 weight %.A wash feed can comprise an alcohol up to 100 weight %. A wash feed cancomprise methanol up to 100%. A wash feed can comprise the same alcoholutilized in the esterification zone 500 for reaction with FDCA to formthe di-ester product. In one embodiment, a wet cake dewatering step canbe used after the wet cake is formed in the solid liquid separation zone300 and before any non-acetic acid wash is employed. This dewateringstep will minimize the liquid content of the wet cake prior to washingwith a non-acetic acid wash solvent such as water and or methanol asdescribed above, thus minimizing the cost to separate any mixtures ofacetic acid and non-acetic acid wash solvents that are generated insolid-liquid separation zone 300.

The solid dicarboxylic acid composition 410, which can be either driedcarboxylic acid solids or wet cake, comprising FDCA, and the alcoholcomposition stream 520 are fed to the esterification reaction zone 500.The solid dicarboxylic acid composition 410 can be shipped via truck,ship, or rail as solids. However, an advantage of the invention is thatthe process for the oxidation of the oxidizable material containing thefuran group can be integrated with the process for the manufacture ofthe crude diester composition.

An integrated process includes co-locating the two manufacturingfacilities, one for oxidation and the other for esterification, within10 miles, or within 5 miles, or within 2 miles, or within 1 mile, orwithin ½ mile of each other. An integrated process also includes havingthe two manufacturing facilities in solid or fluid communication witheach other. If a solid dicarboxylic acid composition is produced, thesolids can be conveyed by any suitable means, such as air or belt, tothe esterification facility. If a wet cake dicarboxylic acid compositionis produced, the wet cake can be moved by belt or pumped as a liquidslurry to the facility for esterification.

The process of the invention is further described in the followingexamples.

Example 1 and 2 Semi-Batch Oxidation of 5-HMF

Air oxidation of 5-HMF using cobalt, manganese and ionic brominecatalysts system in acetic acid solvent in the amounts shown in Table 1were conducted under the following reaction conditions in a reactor setup as described below:

Reactor conditions: 132° C.Reaction pressure: 130 psigReactor set up: a 300 ml autoclave was equipped with a high pressurecondenser, a baffle and an Isco pump. The autoclave was pressurized withapproximately 50 psig of nitrogen and then the homogeneous mixture washeated to the desired temperature in a closed system (i.e., with no gasflow) with stirring. At reaction temperature, an air flow of 1500 sccmwas introduced at the bottom of the solution and the reaction pressurewas adjusted to the desired pressure. A solution of 5-HMF in acetic acidwas fed to the mixture at a rate of 0.833 mL/min via a high pressureIsco pump (this is t=0 for the reaction time). After 30 seconds from thestart of 5-HMF feeding, 1.0 g of peracetic acid in 5.0 mL of acetic acidwas introduced using a blow-case to start the reaction. The feed wasstopped after 1 h and the reaction continued for 1 more hour at the sameconditions of air flow, temperature and pressure. After the reactiontime was completed the air flow was stopped and the autoclave was cooledto room temperature and depressurized. After reaction the heterogeneousmixture was filtered to isolate the crude FDCA. The crude FDCA waswashed with acetic acid two times and then twice with deionized water.The washed crude FDCA was oven dried at 110° C. under vacuum overnight.The solid and the filtrate were analyzed by Gas Chromatography usingBSTFA derivatization method. The b* of the solid was measured using aHunter Ultrascan XE instrument by the following method:1) Assemble the Carver Press die as instructed in the directions—placethe die on the base and place the bottom 40 mm cylinder polished sideface-up.2) Place a 40 mm plastic cup (Chemplex Plasticup, 39.7×6.4 mm) into thedie.3) Fill the cup with the sample to be analyzed. The exact amount ofsample added is not important.4) Place the top 40 mm cylinder polished side face-down on the sample.5) Insert the plunger into the die. No “tilt” should be exhibited in theassembled die.6) Place the die into the Carver Press, making sure that it is near thecenter of the lower platen. Close the safety door.7) Raise the die until the upper platen makes contact with the plunger.Apply >20,000 lbs pressure. Then allow the die to remain under pressurefor approximately 3 minutes (exact time not critical).8) Release the pressure and lower the lower platen holding the die.9) Disassemble the die and remove the cup. Place the cup into a labeledplastic bag (Nasco Whirl-Pak 4 oz).10) Using a HunterLab Colorquest XE colorimeter, create the followingmethod (Hunterlab EasyQuest QC software, version 3.6.2 or later)Mode: RSIN-LAV (Reflectance Specular Included-Large Area View, 8°viewing angle)

Measurements:

CIE L* a* b*

CIE X Y Z

11) Standardize the instrument as prompted by the software using thelight trap accessory and the certified white tile accessory pressedagainst the reflectance port.12) Run a green tile standard using the certified white tile and comparethe CIE X, Y, and Z values obtained against the certified values of thetile. The values obtained should be ±0.15 units on each scale of thestated values.13) Analyze the sample in the bag by pressing it against the reflectanceport and obtaining the spectrum and L*, a*, b* values. Obtain duplicatereadings and average the values for the report.

As shown in Table 1 we have discovered conditions to generate yields ofFDCA up to 89.4%, b*<6, and low carbon burn (<0.0006 mol/min CO+CO2). 1a and 1 b are repeated experiments to show the consistency and smalldeviation in the results. Experiments 2a and 2b are also repeatedexperiments.

TABLE 1 Co Mn Br yield of yield of CO CO₂ Bromide conc conc conc FDCAFFCA (total (total CO_(X) color Example source (ppm) (ppm) (ppm) (%) (%)mol) mol) (mol/min) (b*) 1a solid NaBr 2000 93.3 3000 81.6 0.81 0.0130.078 0.000758 13.91 1b solid NaBr 2000 93.3 3000 82.6 0.87 0.013 0.0920.000875 14.14 2a aqueous 2000 93.3 3000 89.4 0.58 0.003 0.061 0.0005335.85 HBr 2b aqueous 2000 93.3 3000 88.6 0.8 0.0037 0.061 0.000539 6.18HBr *P = 130 psig, CO_(x) (mol/min) = CO (mol/min) + CO2 (mol/min).

Example 3 Synthesis of DMFD

100.0 g of crude FDCA, obtained from a different batch than Example 1but made by the procedure and using the feeds of Example 1 b, was usedas the feedstock. This batch of FDCA contained some FFCA. 410 g of MeOHand the FDCA were mixed in a clean and dry 1 L autoclave at a molarratio of methanol to FDCA of 20:1 and no esterification catalyst wasadded. The autoclave mixture was heated to 180° C. in a closed system tolet the pressure develop. After 3 h at 180° C. the reaction mixture wascooled to room temperature. The volatiles were removed to obtain 114 gof crude product. GC analysis of the crude product showed the followingcomposition: 95.64 wt % of DMFD based on the weight of reaction product,0.50 wt % of 5-(methoxycarbonyl)furan-2-carboxylic acid (MCFC) based onthe weight of product, 1.78 wt % of methyl 5-formylfuran-2-carboxylate(MFFC) based on the weight of product, and 0.74 wt % of water.

Example 4 Solubility of DMFD In Water and Methanol

The solubility of DMFD in water and methanol was tested according to thefollowing procedure: A jacketed 120 ml solubility cells equipped with acondenser, a digital thermometer, a nitrogen blanket and connected to acirculating bath capable of heating/cooling was charged with FDCA andwater or methanol. The heterogeneous mixture was heated to the desiredtemperature and sample was taken using preheated fritted glass pipette.The samples were analyzed using gas chromatography. The results arereported in Tables 3 and 4.

TABLE 3 Measurements of DMFD Solubility (wt %) in Methanol T, ° C. wt %1.0 0.6 14.1 1.4 26.3 2.8 35.3 4.5 46.6 8.7 56.1 15.4 61.3 20.8

TABLE 4 Measurements of DMFD Solubility (wt %) in Water T, ° C. wt % 1.4BDL 13.1 BDL 26.6 BDL 35.6 BDL 47.0 0.1 56.6 0.2 63.9 0.3 74.6 0.4 89.50.9 97.5 1.3 BDL, below detection limit

Example 5 Recrystallization of Crude DMFD Using Methanol

A 150 mL three neck round bottom flask equipped with an overheadstirrer, a nitrogen line and a condenser was charged with 6.0 g of FDMCand 54.0 g of methanol. The solid was dissolved by heating the mixtureto 55° C. The homogenous solution was cooled to 2° C. over a period of 3h. Then the solid was filtered and washed with 20 g methanol pre-chilledto 2° C. two times. It was dried under vacuum overnight. The sameexperiment was repeated at 5° C. and 10° C. The b* of each sample wasmeasured and the results are reported in Table 5.

TABLE 5 Recrystallization of crude DMFD using cold methanol. b* crudeDMFD 5.46 DMFD recrystallized at 10° C. 1.08 DMFD recrystallized at 5°C. 0.86 DMFD recrystallized at 2° C. 0.54

What we claim is:
 1. A dialkyl furan dicarboxylate (DAFD) composition,comprising: (i) at least 98 wt. % solids based on the weight of thecomposition, said solids comprising DAFD in an amount of greater than 98wt. % based on the weight of the solids, (ii) a b* of 5 or less, (iii)not more than 3 wt. % 5-(alkoxycarbonyl)furan-2-carboxylic acid (ACFC),(iv) not more than 3 wt. % alkyl 5-formylfuran-2-carboxylate (AFFC), and(v) not more than 1 wt. % FDCA.
 2. The DAFD composition of claim 1,wherein the DAFD compounds are dimethyl furan dicarboxylate (DMFD), saidDAFD composition further comprising: (i) at least 98 wt. % solids basedon the weight of the composition, said solids comprising DMFD in anamount of greater than 98 wt. % based on the weight of the solids. 3.The DAFD composition of claim 2, comprising: (i) not more than 0.3 wt. %5-(methoxycarbonyl)furan-2-carboxylic acid (MCFC), and (ii) not morethan 0.8 wt. % methyl 5-formylfuran-2-carboxylate (MFFC).
 4. The DAFDcomposition of claim 1, wherein said DAFD composition comprises: (i) notmore than 1000 ppm MCFC, and (ii) not more than 1000 ppm MFFC.